As Carlos Alcaraz sat down in his chair after 90 minutes on Arthur Ashe Stadium, he looked completely perplexed. Alcaraz was not merely having a bad day at the office, he had been utterly horrendous. For nearly two sets, unforced errors had flowed freely from his racket and he did not know how to stop them. A few minutes later, Botic van de Zandschulp held serve to establish a two sets to love lead.

Even as the match rapidly fell away from the No 3 seed, Alcaraz was still the favourite to win, still expected to somehow find a way through as the greatest players always do. But for once in the 21-year-old’s prodigious career, the well had run dry. His inconsistency sharply contrasted with an extremely solid Van de Zandschulp and at the end of an electric night the Dutchman pulled off one of the biggest grand slam upsets in recent years by toppling Alcaraz 6-1, 7-5, 6-4 in the second round of the US Open to set up a match against the British No 1 Jack Draper.

Having established himself as such a reliable performer in the biggest tournaments, this defeat marks the first time that Alcaraz has lost to a player ranked outside of the top 15 at a grand slam since the French Open in 2021, when he was 18 years old and ranked 97th in the world. It is also his earliest loss at a grand slam since that same year.

It was immediately clear that Alcaraz was completely off as Van de Zandschulp rolled through the opening set without issue. Even though he is usually brilliant, Alcaraz can also sometimes be painfully erratic. He was at his very worst here, so often choosing the most unnecessary, complicated shot when simplicity would do and he struggled to land three consecutive groundstrokes all night.

Instead of problem solving and finding a solution, Alcaraz admitted afterwards that he did not know what to do. “He didn’t make a lot of mistakes that I thought he was going to do,” said Alcaraz.

“So I was confused a little bit. I didn’t know how to manage that, how to deal with it. I couldn’t increase my level. I think my level stayed at the same point all the match, and it wasn’t enough to win the match or to give myself the chance of getting into the match or trying to give myself chances.”

Alcaraz had arrived at the US Open, the site of his first grand slam title in 2022, as the player of the summer. His first Roland Garros crown had been quickly followed by a second Wimbledon title and an Olympic silver medal, where only a supreme Novak Djokovic could stop him. Alcaraz admitted that he was tired and feeling the effects of such a busy summer but he also needs to make significant improvements mentally.

“Today I was playing against the opponent, and I was playing against myself in my mind,” said Alcaraz. “A lot of emotions that I couldn’t control. It was kind of … I was up in some points, then I lose some points; I get down. It was a rollercoaster, let’s say, in my mind. So I can’t be like that if I want to think about [winning] big things, so I have to improve.”

He was also outplayed by a brilliant opponent who finally demonstrated his talents on one of the biggest stages. The Dutchman was everywhere; his athleticism and defence playing a significant role in Alcaraz’s discomfort, he commanded the baseline with his forehand and he was brilliant in the forecourt, frequently beating Alcaraz to the net. In the final set, as Alcaraz tried to pull himself back into contention, Van de Zandschulp held his nerve and closed out the win.

Three months ago, there was a chance that Van de Zandschulp might not even be at the US Open in any form. A formidable player who reached a career-high ranking of No 22 two years ago, his head has so often been his biggest obstacle and he is usually a picture of misery on the court. After a listless first-round loss in straight sets at the French Open, the Dutchman admitted he was considering retirement.

“At the time I said it, I was thinking about it, of course,” he said. “It was just more the way things were going. I got injured last year. Still had some troubles with the injury from last year. That was for me like if I have to keep playing with the pain I had, yeah, then there was a chance maybe I would stop playing.”

It took a significant amount of effort for Van de Zandschulp to find his way back on to the right path, including dropping back down to ATP Challenger events after his ranking tumbled and rebuilding from scratch. Now he has toppled the great Alcaraz in one of the biggest tournaments in the world.

Asked about his emotions after such an enormous achievement, Van de Zandschulp laughed: “Actually right now not so many. Yeah, maybe I’m still processing it. Maybe in a couple of hours or tomorrow I [will] feel a little bit more emotional with what happened tonight.”